1. Technical Field
This invention relates to oil spill remediation and cleanup techniques where porous materials with oil-absorbing capabilities can be widely utilized.
2. Description of the Related Art
From Exxon-Valdez in 1989 to the more recent Deepwater Horizon in 2010, oil spills rank among the worst human-induced disasters our earth can face both environmentally and economically. The onset of these spills is extremely difficult, if not impossible, to predict in advance, and thus preventative measures are tough to institute. The next best thing is to minimize the lasting effects of oil spills by using effective remediation methods.
Right now, there are five major oil spill remediation methods that are in wide use: bioremediation, containment, dispersion, in situ burning, and skimming [1, 2, 3, 4].
Bioremediation involves using bacteria as well as other microorganisms that consume oil as part of their daily life to clean up the oil spill. Bacteria are living organisms, and they can perish due to unfavorable environmental conditions (bad weather, for example). Furthermore, bacteria remove oil extremely slowly. In many cases, the process of oil removal is too slow for bioremediation to be an effective cleanup technique.
Containment methods use large rubber booms to encircle the oil spill. The booms prevent further spreading of the oil, at least in the short-term. However, with time, the oil begins to form channels underneath and through crevices in the booms, and the oil begins to spread beyond the booms. Note that the booms do not absorb any oil, they just redirect it.
Dispersion involves using ships, planes, or helicopters, to spray dispersants on top of the oil spill. Dispersants allow oil and water, two previously immiscible liquids, to mix. The dispersants break the oil up into smaller pools. Dispersants cause problems though because the oil is not really removed—it has simply been integrated with the environment underneath, just removed from the surface. After some time, the oil integrated into the water harms the local ecosystems, and affects the economies that depend on the welfare of those aquatic ecosystems such as the fishing industry. Also, the dispersants are man-made chemicals that can be harmful to the aquatic ecosystems.
In situ burning involves using containment booms to separate a small pool of oil from the general sheet of oil spill, and then lighting the small pool of oil on fire. It is extremely effective at removing oil. However, by burning isolated slicks of oil, we may be solving one environmental problem, but we are drastically aggravating the another problem, namely global warming [6,7,8].
Skimming involves attaching machinery to boats and other ocean vessels that can, as the name of the practice suggests, skim oil right off of the surface of the water. The problem with skimming is that the technology only functions optimally in calm weather—if the water is turbulent and the environment windy, which in fact is extremely characteristic of the Gulf area in which the Deepwater Horizon oil spill took place, the surface is not necessarily just oil because the turbulence serves to “break” the sheet of oil on the top, and then the skimmer will then be skimming and filtering a mixture of oil and water.
Clearly, due to the limitations of current methods available for oil spill remediation, there is a massive effort to discover new and different methods [4, 5, 6, 7, 8]. Of late, researchers across the world have started focusing on a new method of oil spill remediation: the use of oil-absorbing porous materials. For example, a group of researchers in China have recently developed oleophilic carbon nanotube fibers that are capable of absorbing inordinate amounts of oil [7]. However, as with any new and aspiring technology, there are no systems available for measuring the efficacy of these porous materials in oil spill cleanup.
Note that most porous materials in the industry, including sol-gels, were not designed for use in oil spill remediation. The most common test of the absorbance of a porous material is to simply introduce the porous material into a given mixture of water and oil, and then allow the material to remain stagnant for a set period of time while it absorbs the oil. Such a measurement strategy is fine for common applications of porous materials, like paper towels.
However, a test where the porous material and the mixture are both stationary is not useful to identify porous materials that can be effective in oil-spill cleanups. We observed that the oil-absorbing capability (amount of absorption as well as the rate or absorption) of new porous materials like sol-gels depends on several factors like the type of motion the oil and water mixture is being subjected to by the environment, the wind patterns and air pressure, and the relative motion of the porous material and the mixture of oil and water.